1. Field of the Invention
The present invention relates to an improved fiber optic holding fixture for an optical interferometer. In particular, the present invention relates to an improved fiber optic holding fixture for holding within an optical interferometer, a connector ferrule or a combination of an optical fiber end surrounded by a connector ferrule, which interferometer is suitable for inspecting the symmetry and geometry of an end face of said combined optical fiber and connector ferrule, said fiber optic holding fixture comprising:
a holding plate suitable for use in an optical interferometer; PA1 holding means for holding in a precision, repeatable orientation, with reference to an interferometric reference surface, a connector ferrule or an end of an optical fiber connection comprising an optical fiber end surrounded by a connector ferrule, which holding means comprises a vee-shaped groove in said holding plate providing contact on two points of the circumference of said connector ferrule, PA1 a clamping means integrally formed within said holding plate and cooperating with said holding means, said clamping means permiting the selective application of force against a third point on the circumference of said connector ferrule held in position within said vee-shaped groove of said holding means; and, PA1 operating means located remotely from said vee-shaped groove and permitting the selective application of force by said clamping means against a third point on the circumference of said connector ferrule held in position within said vee-shaped groove of said holding means by said clamping means. PA1 a. preparing an end of a connector ferrule or an optical fiber surrounded by a connector ferrule for the purpose of connection, such as with a mating optical fiber prepared for connection; PA1 b. placing said prepared connector ferrule or optical fiber end within an improved fiber optic holding fixture for holding within an optical interferometer, which interferometer is suitable for inspecting the symmetry and geometry of an end face of said connector ferrule or combined optical fiber and connector ferrule, said fiber optic holding fixture comprising: PA1 a clamping means integrally formed within said holding plate and cooperating with said holding means, said clamping means permiting the selective application of force against a third point on the circumference of said connector ferrule held in position within said vee-shaped groove of said holding means; and, PA1 operating means located remotely from said vee-shaped groove and permitting the selective application of force by said clamping means against a third point on the circumference of said connector ferrule held in position within said vee-shaped groove of said holding means by said clamping means; PA1 c. engaging said clamping means through the operation of said operating means; PA1 d. inspecting the symmetry and geometry of the prepared end of said connector ferrule or combination of an optical fiber end surrounded by a connector ferrule with said optical interferometer for connection suitability. PA1 a holding plate suitable for use in an optical interferometer; PA1 holding means for holding in a precision, repeatable orientation, with reference to an interferometric reference surface, a connector ferrule or an end of an optical fiber connection comprising an optical fiber end surrounded by a connector ferrule, which holding means comprises a vee-shaped groove in said holding plate providing contact on two points of the circumference of said connector ferrule, PA1 a clamping means integrally formed within said holding plate and cooperating with said holding means, said clamping means permiting the selective application of force against a third point on the circumference of said connector ferrule held in position within said vee-shaped groove of said holding means; and, PA1 operating means located remotely from said vee-shaped groove and permitting the selective application of force by said clamping means against a third point on the circumference of said connector ferrule held in position within said vee-shaped groove of said holding means by said clamping means. PA1 a. preparing an end of a connector ferrule or an optical fiber surrounded by a connector ferrule for the purpose of connection, such as with a mating optical fiber prepared for connection; PA1 b. placing said prepared end of said connector ferrule or combination of optical fiber within a connector ferrule within an improved fiber optic holding fixture for holding within an optical interferometer, which interferometer is suitable for inspecting the symmetry and geometry of an end face of said connector ferrule or combined optical fiber and connector ferrule, said fiber optic holding fixture comprising: PA1 a clamping means integrally formed within said holding plate and cooperating with said holding means, said clamping means permiting the selective application of force against a third point on the circumference of said connector ferrule held in position within said vee-shaped groove of said holding means; and, PA1 operating means located remotely from said vee-shaped groove and permitting the selective application of force by said clamping means against a third point on the circumference of said connector ferrule held in position within said vee-shaped groove of said holding means by said clamping means; PA1 c. engaging said clamping means through the operation of said operating means; PA1 d. inspecting the symmetry and geometry of the prepared end of said connector ferrule or combination of an optical fiber end surrounded by a connector ferrule with said optical interferometer for connection suitability.
and wherein the improvement comprises:
According to another embodiment of the present invention, there is provided a method for inspecting the symmetry and geometry of a connector ferrule or a combination of an optical fiber end surrounded by a connector ferrule, with an optical interferometer, said method comprising the steps of:
a holding plate suitable for use in an optical interferometer; PA2 holding means for holding in a precision, repeatable orientation, with reference to an interferometric reference surface, an end of an optical fiber connection comprising a connector ferrule or an optical fiber end surrounded by a connector ferrule, which holding means comprises a vee-shaped groove in said holding plate providing contact on two points of the circumference of said connector ferrule, PA2 a holding plate suitable for use in an optical interferometer; PA2 holding means for holding in a precision, repeatable orientation, with reference to an interferometric reference surface, a connector ferrule or an end of an optical fiber connection comprising an optical fiber end surrounded by a connector ferrule, which holding means comprises a vee-shaped groove in said holding plate providing contact on two points of the circumference of said connector ferrule,
and wherein the improvement comprises:
2. Description of Related Art
There has long been a need to inspect the end of a fiber optic connector for information on the geometry of the end face in the control of the polishing process and to confirm quality for assurance of performance in an application. Typical parameters to be measured are: radius of curvature of the ferrule and fiber end, symmetry of polish, and undercut or protrusion of the fiber with reference to the ferrule surface.
Interferometry is one of the preferred methods for measuring the surface of the connector because the fringe pattern provides three dimensional information about the surface of the connection, and allows the parameters to estimated or calcalulated. In order to use interferrometry to inspect for the symetry of the polish, however, it is necessary to hold the connector in a known position which is both precise and repeatable, and typically perpendicular, with respect to the reference surface, in an interferometer. This precision positioning is necessary to provide consistent reproducible measurements whenever a connector is inserted into a measuring instrument.
For example, Physical contact (PC) polished connectors having a hemispherical or dome shaped endface are intended to be polished so that the optical fiber is at the peak of the dome. When two PC polished connector are brought into contact, the fibers are the first to meet. This allows the fibers to compress slightly to form an intimate optical contact which minimizes reflections at the interface. In order to guarantee that the fibers make the first contact, a typical standard for symmetry allows the peak of the polish to be a maximum of about fifty (50) microns from the center of the fiber.
Because of the tight tolerences required in the manufacturing process, and the need to hold such tolerances on the micron level, the slightest variation in ferrule position from a centered, precise and repeatable axis with respect to the reference surface will lead to varying measurements depending on the rotation of the ferrule around the actual axis.
In the prior art, this problem has been addressed with some success by providing a holding plate with a precision bore hole. However, this solution requires both the hole of the holding plate and the ferrule of a connector to both be within a micron of one another. While some success has been obtained in this way, the machining of such tight tolerances on a consistant basis has been difficult and the useful lifetimes of such precision bore holes has been limited by wear.
Another method which has had some success is a holding plate with a clamping arm, in which a vee-groove through the plate provides support and centering for two points on the circumference of a ferrule, while a clamping arm provides a third point in a three-point contact. This arm may be designed as a bar attached to both sides of a vee groove with screws to apply holding pressure. Alternatively, one side of the clamping arm may be hinged and the other side locked in place with a screw or clamp. Another alternative could be that the hinged arm may be spring-biased. While such a construction can provide the necessary accuracy in many cases, it is often unwieldy for a production environment or complicated and expensive in design.